Polishing P20 vs P20+Ni Mold Steel | How to Achieve a Mirror Finish

P20+Ni because contains 1% Ni, density better but slightly harder to polish.

Mirror processing suggestion: pre-grind to #1200 sandpaper, then use 3µm, 1µm diamond paste step-by-step polish, rotation speed 3000–6000rpm, pressure <0.2MPa, cooperate with kerosene or special polishing liquid, finally use 0.05µm aluminum oxide fine polish, can reach Ra≤0.02µm mirror effect.

P20 vs. P20+Ni

P20 Advantage & Limitation

P20 steel pulled back into factory even quenching furnace no need enter, itself carries 28 to 32 degrees pre-hard foundation. CNC milling machine installed with blade pulls rotation speed to per minute 1500 revolutions, feed speed pushed to 800 millimeters per minute. Processing long 600 millimeters, wide 400 millimeters TV back cover mold, machine runs not reaching 35 hours can deliver rough blank.

Steelmaking master stuck carbon content in formula at 0.38% up and down, into inside mixed in 1.5% chromium element, maintaining most basic mechanical foundation. Purchasing department went to steel market pull goods, per ton P20 compared to high-grade steel types saved 3000 to 5000 bucks. Factory received a hit 50,000 plastic basins order, just buying steel's expense abruptly cut down 20%.

· Rough processing milling single side leaves 0.5 millimeter margin

· Fine processing depth of cut dead dead pressed in 0.15 millimeter inside

· Drilling machine tool spindle set 800 revolutions

· Machine tapping torque absolutely not exceeds 30 Newton meters

Steel rolling mill forged thickness covering over 250 millimeters P20 big board, outside completely cooled, inside still hot. Sawing machine cuts thick board one divide into two, takes hardness tester towards edge a knock has 31 degrees, probe towards board center moves 200 millimeters, number cliff drops to 24 degrees even 22 degrees. Microscope under, internal structure clumping's width runs to 3 micrometers upwards.

800-ton injection molding machine every day takes high pressure towards mold cavity inside smashes. P20 middle biased soft area hard carries tens of thousands times impact, surface quietly towards back retreated 0.02 to 0.05 millimeters. Hit out plastic parts edge entirely is a circle flash, watch machine's young man only can take holding pressure time from 8 seconds drag to 12 seconds, burr same as before scratches hands.

Fitter takes 600 grit sandpaper in cavity inside back and forth rubs, surface looks quite bright. Changes onto 1200 grit, 2000 grit fine sandpaper, then smears on particle size 3.5 micrometers diamond polishing paste forcibly towards down presses. Magnifying glass a shine, steel surface entirely is 0.08 millimeters wide wave pits. Inside hiding's aluminum oxide inclusions by cloth wheel pulled out, left behind a piece 0.05 millimeters deep sand holes.

· Polishing stretched to death reaches SPI standard's B2 level

· Surface roughness probe reading stuck at 0.1 micrometers down not go

· Polishing cloth wheel one minute turns over 2000 circles surface turns yellow burns

· Polishing master at one point stays absolutely not exceeds 4 seconds

Drawing on written mold lifespan 300,000 times, workshop hits to 150,000 times, cavity surface bright light naked eye visibly turns dark. Design alteration needs take argon arc welding repair material, welding gun instantly sprays out 1500 degrees high temperature. Base material not put into fire furnace inside in advance heated to 200 degrees, flaw detector towards weld seam surrounding a sweep, entirely are long 5 millimeters, wide 0.01 millimeters fine micro cracks.

For washing machine inner tub base open mold, outer surface needs do VDI standard's number 24 skin texture, take P20 do work fairly handy. Formulated good nitric acid and iron trichloride acid water poured on surface, bitten out pattern fully has 0.04 millimeters deep. Potholed skin texture a cover, steel hit not bright's defect was covered tightly and solidly.

· Only receive VDI number 24 upwards rough skin texture parts

· Do hiding in machine inside cannot be seen skeleton support parts

· Boss requires 25 days must deliver goods urgent order

· Mold total expense dead dead stuck in 50,000 bucks inside's low price order

Customer brings over transparent PC lamp cover drawing, light transmittance indicator fixed dead at 92%. Polishing master pressed P20 cavity continuously did 60 hours' physical labor. Injection molding machine hits out transparent parts suffused with a layer white misty fog water, light rays hit on 0.1 micrometers high low uneven micro surface flies randomly, luminous flux abruptly runs away 15%.

Sulfur content rushes to 0.03%'s normal P20, inside's manganese sulfide dregs pulled into 50 micrometers long strips. Milling cutter cuts to these hard blocks often chips off a piece edge, mold demolding friction coefficient vividly raised high 0.15. Ejector pin takes product pushes out that one instant, plastic part on strangles out one stripe stripe white ejector white marks, a basket products scrapped 18%.

Take P20 moved to electroplating tank hang a layer 0.02 millimeters thick hard chrome protection. Electroplating water temperature burns to 55 degrees, ammeter hits to per square decimeter 40 amperes. Base body only has 30 degrees hardness, fundamentally support not hold outside that layer hard shell. Machine changes onto mixed 30% glass fiber nylon material, continuously hits 20,000 times, inside's chrome plating layer slice by slice towards down drops.

Tolerance requires 0.01 millimeters precision gear mold, P20 inside's internal stress entirely at dark place exerts force. Wire cutting machine tool cuts down a piece 60 millimeters thick material, placed on flat table air dried 48 hours. Dial indicator needle head next to surface a slide, two ends warp up 0.03 millimeters. Fitter master squats at table front extra consumes 6 hours grind flat contact surface, upper lower mold just tightly seamless clasped together.

P20+Ni Parameters & Mirror Surface

Steelmaking furnace inside towards steel water adds in 0.9% to 1.2% nickel element, whole furnace steel's temper thoroughly changed. This furnace grade 1.2738's P20+Ni steel water cast into 800 millimeters thick big block, cooling speed was forcibly dragged slow. Thick board from outer skin to deepest place's center position, hardness tester hits out reading dead dead bites in HRC 29 to 33 between. Steel profile's hardness drop stubbornly squeezed to not sufficient 2 degrees.

Placed 500 times microscope under looks section, inside's tempered sorbite squeezed densely packed, grain size stable at 8 level above. Lathe depth of cut opens to 0.2 millimeters towards down cuts, discharged out iron chips entirely are continuous uninterrupted spiral long strips. Nickel element took steel's toughness towards up dragged a section, 12 millimeters milling cutter by per minute 1200 revolutions speed opens rough, cutter head chipping's probability large margin drops.

Do car light lens mold, fitter master first takes 400 grit oilstone takes CNC machine tool left behind's cutter marks thoroughly pushes flat. Changes onto 800 grit then to 1500 grit imported sandpaper, horizontal vertical crossing polishes surface. P20+Ni's foundation enough hard enough solid, sandpaper in cavity inside back and forth walks 200 trips, steel surface still stands tall and straight, absolutely not will appear locally collapsed down's soft points.

Enters high-level polishing stage, wool felt smears on particle size W1.5 (equivalent to 8000 grit)'s diamond grinding paste. Polishing machine adjusts to per minute 1800 revolutions towards steel on presses, one continuous pushes on 5 hours. Base body inside no impurities debris was brought out, surface roughness Ra value steadily drops through 0.02 micrometers. Light hits on, cavity just like a face smooth mirror.

· Polishing standard takes down SPI association's A2 to A3 level

· Ra probe measures out roughness all year round sticks at 0.015 micrometers

· Diamond paste grinding single time operation allowed stay extend to 8 seconds

· Wool wheel high speed friction surface temperature rises to 60 degrees not leave yellow spots

Customer inspects factory takes strong light flashlight sticking to car headlight's injection molded part shines, light transmittance instrument screen on jumps out 93.5% data. P20+Ni cavity pressed out's PC transparent part, light penetration extremely excellent, cannot find one thread diffuse reflection's fog feeling. Injection molding machine every day maintains 2000 mold times's high load operation, continuously hits full three months, mold surface glossiness even 10%'s attenuation all measure not to.

Normal materials fear cloth wheel excessive cutting makes out wave marks, P20+Ni's microscopic structure like a solid brick wall. Polishing worker hand on's strength even if bigger 20 Newtons, surface same as before is a straight line. Before those long wide 0.05 millimeters' annoying sand holes thoroughly go extinct, mold factory again also no need for polishing failure anew onto machine tool takes cavity mills away one layer.

Workshop production schedule list on, these two pieces materials' processing account book calculated clearly clearly.

Argon arc welding machine current hits to 120 amperes, welding rod in steel on melts out 10 millimeters wide weld seam. Cooling after takes ultrasonic flaw detector sweeps one circle, weld seam with base material bites closely closely firmly firmly, surrounding cannot find even if 0.02 millimeters dark crack.

Demolding draft angle stuck at merely 0.5 degrees limit design, cavity's smoothness helped big busy. Injection molding machine pulls open mold, ejector pin applies 400 kilograms thrust, transparent PC part smoothly pops out. Surface no fine potholes friction, product edge cannot find turning white stress marks, workshop inspector takes injection molding good product rate's board directly rewrites to 98.5%.

Step-by-Step Guide

Preparation & Roughing

Crane takes 350 kilograms heavy injection mold core horizontally translates hoists to fitter table on, steel block surface sticky, entirely is turning yellow sulfurized cutting oil. This layer approximately 0.02 millimeters thick oil film extremely sucks dust, even air inside Mohs hardness 7 level quartz sand micro particles all will stick on. Take spray pot fill full industrial purity 99.8% isopropyl alcohol facing sprays, tear piece dust-free cloth clockwise direction uses force wipes three times.

Front walked CNC milling machine time depth of cut set 0.15 millimeters, cutter head friction lets surface layer steel instantly soar to 800 degrees Celsius. Cooling after just leaves a layer thick about 0.03 millimeters hardened white layer. Normal P20 test block in Rockwell hardness tester on hits out is 30 HRC, white layer area value soars to 52 HRC. If is electrical discharge machining, white layer can reach 0.05 millimeters thick, take high power microscope look, covered full deep 5 micrometers micro cracks.

From tool cabinet takes a handful 320 grit silicon carbide oilstone, long 150 millimeters, wide 13 millimeters, thick 6 millimeters. Takes a plastic plate pours full aviation kerosene, takes whole root oilstone soaks go in immerse 5 minutes. Water surface on gurgling emits bubbles, must take oilstone internal 25% pores inside's air all discharge clean. If takes dry oilstone hard pushes, cutting surface on's grinding particles instantly block dead, local friction produces 400 degrees Celsius high temperature takes steel burns black.

Grinding hand feeling all relies on two hands cooperate to control material cutting amount:

· Right hand thumb dead dead presses hold oilstone front end 30 millimeters place.

· Left hand wrist carries walking, push pull stroke pressed in 45 millimeters to 60 millimeters between.

· Do work frequency stable at per minute 120 times up down.

· Oilstone bottom surface and mold surface included angle bites dead at 15 degrees.

Pushes P20 steel time, hand back muscles can feel slight blockage feeling. Steel mill forging time carbon element distribution even if differ 0.05%, steel material inside just will have band-shaped soft zones. Two hands press down's torque must stable at 3.5 Newtons. Wrist slightly stiffens a bit exerts force not even, just takes those soft zones planes out deep 0.01 millimeters wave pits.

Changes into processing P20+Ni steel material, inside mixed 0.9% to 1.2%'s nickel element, austenite grain size reaches 8 level. Still uses 3.5 Newtons strength goes push, hearing friction sound from ear-piercing ka-ka sound changed into muffled sha-sha sound. Pushes finish 100 square millimeters area, takes dry cloth a wipe, steel surface reveals very uniform silver gray frosted texture.

Dropped down's silicon carbide particles mixed with iron chips, turn into black black oil mud, stuff full 0.005 millimeters wide grinding grain lines. Takes air gun takes air pressure adjusts to 0.6 MPa starts blow sweeping. Brass wind nozzle leaves steel board surface 15 millimeters, per second walks 50 millimeters. Hand-held type surface roughness instrument sticks on, diamond measuring needle uniform speed slides past 0.8 millimeters sampling length. Screen one flash displays Ra value 0.65 micrometers, original deep 0.08 millimeters milling cutter marks all ground flat.

Bumps into deep cavity inside R3 millimeters round corner, just now square oilstone edge corner extremely easy scratches rotten beside's smooth surface. Find a root diameter 6 millimeters red aluminum oxide fiber oilstone, stuff into pneumatic ultrasonic polishing machine chuck inside. Knob dials to per second 25000 times vibration, back and forth expansion contraction physical stroke set at 0.3 millimeters.

In narrow gap inside rough grinding slightly not keep attention just will cut waste, hand on's pneumatic tool parameters execute as follows hard standards:

· Air inlet pipe end head air pressure stuck dead at 0.4 MPa.

· Fiber head against steel's strength not exceeds 150 grams.

· At same one point position stay absolutely not exceeds 2 seconds.

· Front end wears drop 1 millimeter immediately changes new.

Wears on brings 3.5 times optical resin lens's head-mounted magnifying glass, head top's LED cold white light source adjusts to 45 degrees angle hits towards mold surface. Two eyes stare at steel board reflects light's place, find those solitary small bright points. As long as sees one diameter 0.05 millimeters bright point, underneath just hides not ground to bottom's electrical discharge pockmarks. Takes writing brush dips one drop kerosene points on, facing that position honestly again pushes 30 times.

Sequential Sanding

From left side consumables cabinet bottom layer pulls out a whole sheet 230 millimeters multiply 280 millimeters German produced 400 grit water sandpaper. Takes utility knife follows back side paper base texture, cuts out long strip shaped sandpaper pieces, width uses steel board ruler stuck dead at 15 millimeters. Find a piece thickness 8 millimeters hard cork board act as bottom pad, takes cut good sandpaper pieces flatly wrap at wood board front end working surface.

Start hand grinding's direction, compulsorily requires with just now oilstone walked's grain lines form 90 degrees vertical cross. Wrist exerts force carries cork pad on steel surface flat pushes, single time push pull stroke maintains at 50 millimeters around. 400 grit silicon carbide grinding particles on metal surface layer cut, a few down just squeeze out black gray color metal mud. Operator eyes must dead dead stare at steel surface reflects light place, until previous pass oilstone left behind's 0.05 millimeters deep scratches completely by new vertical texture covered.

Do finish this pass must stop hand on's work, rush progress go take 600 grit sandpaper will destroy whole block steel board. Takes large size cotton ball dips full purity 95% industrial isopropyl alcohol, takes mold core on residual's black color metal powder entirely wipe remove. Fitter table surface uses wet cloth sweeps one pass, even operator's two hands all must arrive water tap under uses soap rubs washes half minute. One piece 400 grit's detached grinding particle approximately has 35 micrometers big, mixes into next pass working sequence, will on 1000 grit surface plow out one stripe deep 0.02 millimeters bright scratch.

Ensure surrounding environment and table surface thoroughly clean after, wraps on 600 grit sandpaper, push pull direction once again on steel board flat surface rotates 90 degrees. On sandpaper working surface drips two drops low viscosity's special grinding oil. Oil liquid can rapidly carry away cut down's micro small iron chips, prevent sandpaper particles gap being blocked dead generating heat. Push pull's action frequency slows down to per minute 80 times, wrist applied down press weight from 2.5 kilograms weakens to approximately 1.5 kilograms.

Pushes to 800 grit stage, steel board underneath's material temper thoroughly exposed on hand feeling. Pushes P20 steel time, push travel resistance occasionally appears instant's jumping, internal ferrite and pearlite hardness different brought cutting drop. Meets reflecting light turning white's micro small hard point areas, fingers towards down press's strength temporarily increases about 200 grams. P20+Ni mixed in about 1%'s nickel element, overall hardness fluctuation extremely small, grinding resistance constantly maintains at about 12 Newtons.

Enters 1000 grit and 1200 grit, bottom part's support pad material faces compulsory replacement. Throws away just now that piece 8 millimeters cork board, changes into thickness 3 millimeters high density acrylic strip, outside first wraps a layer thin thin pure cotton cloth. This time sandpaper surface silicon carbide grinding particles' diameter dropped to 15 micrometers below, cutting force extremely weak. Same one piece sandpaper's usage lifespan shortened to 3 minutes inside, grinding particles become blunt after on steel surface dry rubs will produce 300℃ local instant high temperature.

Sandpaper cross number alternating operation rules:

· Strictly forbid jumping numbers operation.

· Compulsorily execute 90 degrees crossing.

· Cover previous pass scratches see bottom.

· Consumables replacement must wash both hands.

Edge prevent collapse angle control shape rules:

· Edge receiving force halved output.

· Suspended outward extension stuck dead 5 millimeters.

· Acrylic pad board replaces cork.

· Horizontal translation overlap rate stable at 20%.

Sprint 1500 grit last pass defense line, dripped on steel surface's lubricating liquid changes into viscosity only 5 cSt ultra thin aviation kerosene mixed liquid. Two hands basically not extra exert force, entirely relying on tool and hand part naturally dropping down's about 800 grams weight on surface slides. Head top's cold white light fluorescent lamp tube shines on mold surface, steel material originally gray dark frosted surface starts reveal extremely weak metal reflection. Probe goes up runs one circle 0.8 millimeters measuring stroke, surface's Ra value steadily dropped to 0.15 micrometers.

Different thick thin sandpaper grinding time's receiving force and consumption parameters table:

Old sandpaper depleted thrown into waste bucket, facing mold surface sprays on large amount cleaning agent, takes brass air gun sticks close fiercely blows. Surface strictly forbidden leave one thread oil film and fine micro dust. P20 or P20+Ni steel surface touches up slippery, like is covered with a layer extremely fine delicate white fog. Unplugs air gun pipe, pushes away fitter table on's debris, takes polishing machine's power cord plug presses into 220V socket, prepares deal with that layer 0.15 micrometers roughness's white fog.

Diamond Paste Polishing

Work table on air gun pipe unplugged hung back iron rack, anti-static rubber pad on only leaves a branch 10 milliliters capacity, loaded full 9 micrometers diamond grinding paste's plastic syringe. Thumb push rod squeezes out about 0.5 grams light blue color paste body, evenly point applies on long wide each 100 millimeters mold steel board. Takes a piece diameter 25 millimeters, thickness 12 millimeters extra hard wool felt wheel, stuck into pneumatic hanging grinder's three jaw chuck inside. Foot pedal switch steps down, machine rotation speed instantly soars to 6000 revolutions/minute.

Wool felt wheel dead dead presses on steel surface, paste body inside's polyhedron artificial diamond micro particles by strong force crushed scatter open. Operating hand towards felt wheel on applies about 1.5 kilograms down press force, following "Z" character shape trajectory on mold core uniform speed horizontally sweeps. Violent friction lets grinding area's temperature within 10 seconds from room temperature 25℃ dry pulled to 60℃ above. Steel board surface 1500 grit sandpaper left behind's 0.15 micrometers roughness white fog, by hard vivid stripped off one layer skin.

Takes high gram weight absorbent cotton ball dipping extremely easy volatilize special wash mold water wipes dry surface. Originally foggy steel material starts pan out bottom light, can blurrily reflect out head top fluorescent lamp tube's white long strip. Takes portable roughness probe rests up measures a bit, Ra value cliff style dropped to 0.05 micrometers. Wears 3 times magnifying glass approaches closely finds, if discovers remaining even if one stripe 0.02 millimeters wide crossing net lines, must original position squeeze point blue paste heavy polish one pass.

Clear empty table surface changes onto holding 3 micrometers yellow grinding paste's needle tube. Bumps into normal P20 steel material, hand on's parameters must dead dead press hold. Unplug hard wool felt, change onto medium hardness short plush cloth wheel, rotation speed compulsorily drops to 2500 revolutions/minute inside. Two hands towards down press's strength absolutely cannot exceed 1 kilogram, underneath's local temperature once burns pass 150℃ just wants provoke big trouble.

Normal P20 steel inside ferrite and pearlite mixed, receiving heat expansion coefficient completely different. Rotation speed leans fast or presses too ruthlessly, leaning soft ferrite is dug empty, leaning hard pearlite all bulges at outside. Naked eye sticking to reflecting light surface looks, flat steel surface on will float appear a piece densely packed concave pits, with ripe thorough orange peel exactly same. Really produced orange peel rise fall, only can retreat back 800 grit water sandpaper, back and forth push pull about 400 times, go strip off that 0.02 millimeters waste material.

Changes into grinding P20+Ni steel block, polishing machine handle transmitted coming resistance feedback completely changed. Internal mixed in 1% nickel element takes bottom material solidifies very evenly, even if operating wrist pressed to 1.2 kilograms same as before raises light. 3 micrometers yellow paste in plush cloth wheel underneath walks 3 minutes, wipe dry after steel surface brightened up. Takes a handful bearing 0.02 millimeters graduation lines' vernier caliper stands at beside, fine dense graduation numbers clearly reflected in steel board inside.

Each level paste body consumption and physical control shape data:

· 9 micrometers laying bottom: per square centimeter consumes paste 0.05 grams, pairs hard wool felt strong force pulls lines.

· 3 micrometers transition: rotation speed pressed dead under 3000 revolutions, pairs short plush cloth eliminates fog feeling.

· 1 micrometer collecting light: down press force reduces to 300 grams inside, pairs extremely soft absorbent cotton forces out reflection.

Leaving highest level SPI A-2 level mirror surface only remains last pass gate limit. Unplugs plush cloth wheel, changes onto pressed tightly tightly medical grade long staple absorbent cotton. Squeezes out weight only about 0.1 grams 1 micrometer white color diamond paste. Rotation speed meter pointer adjusts to extremely low 800 revolutions/minute, two hands almost suspended empty, only borrowing cotton flower ball self carrying's 50 grams weight on steel surface extremely lightly draws small circles.

Dealing with P20+Ni material has a strict severe high voltage line. Steel material exiting factory carrying's trace amounts sulfides non-metal impurities, under 1 micrometer extremely fine grinding particles specially sensitive. At same one position polishing drawing circles staying exceeds 15 seconds, impurity particles will be vividly peeled off.

Even if drops out a diameter only having 10 micrometers inclusion, high brightness mirror surface on just will add one uses kerosene all soaking also washes not off's dead black point. Seeing metal reflection edge sharp not scatter light, immediately lift hand stop machine.

Takes a sheet newly unsealed lens paper drips two drops absolute ethanol, following single one direction lightly scratches past steel surface. Placed inspection lamp under uses 10 times magnifying glass sweeps looks, surface Ra value approaches 0.01 micrometers. Fingers suspended at mold above 50 millimeters place, metal surface reflected out's fingerprints even 0.1 millimeters flesh grooves all clear clear. Whole factory building's roof ceiling steel beam structure, all entirely completely gathered into a piece 100 square centimeters mold steel board inside.

Pitting & Orange Peel

Orange Peel

Master hand in's wool felt by per minute 3000 revolutions rotation speed sticking mold rubs. Not reaching twenty seconds, steel board surface's temperature breaks through 150 degrees Celsius. Hand in adding heavy force once crosses 2.5 kilograms/square centimeter's boundary, steel material surface layer rises falls. Soft's place by high temperature softened, hard's place bulges up, high low drop exceeding 0.005 millimeters wave grain lines immediately show appear.

Looks looks this piece steel material's internal composition table. Carbon content at 0.35% to 0.45% between floats moves. Cooperating 1.4% to 2.0% chromium element, iron block inside grows out hardness not same spots blocks. Conventional exiting factory normal P20 steel board thickness only needs exceed 400 millimeters, center area's hardness often only has 28 HRC.

Soft hard alternating spots blocks facing grinding tools cutting, depletion speed completely not same.

· 800 number oilstone push grinding cutting amount in 0.02 millimeters inside

· 1200 number sandpaper dry grinding extremely easy produces heat gathering

· 15 micrometers diamond paste needs maintain extremely light press feeling

· Wool wheel rotation speed strictly avoid exceeding 5000 revolutions/minute

Added 0.8% to 1.2% nickel element's P20+Ni placed on same one work station on. Nickel element drills into iron atoms' gaps inside. Whole piece 600 millimeters thick steel board center hardness supports bottom at 30 HRC above. Hardness drop shrinks small to 2 HRC inside, grinding tools walked past's resistance becomes unusually uniform.

Polishing machine stays at same one place exceeding fifteen minutes is extremely terrible operation. Continuous rubbing lets heat amount pile up emit heat. Polishing paste inside's grinding liquid under 120 degrees above high temperature volatilizes into smoke. Dry astringent polishing wheel carrying remaining 3 micrometers diamond particles at steel board surface hard gnaws.

Relying on naked eye discovers these wave rises falls needs specific techniques and tools cooperate.

· Uses 2000 lumens single light source cold light lamp side light shines

· Line of sight and mold surface maintain 15 degrees low angle flat look

· Anti-rust oil smear thickness controlled at 2 micrometers around

· Uses 60 times hand-held magnifying glass observes wave peaks wave valleys

· Compare standard SPI A3 sample block reflectivity differences

Already formed 0.01 millimeters drop's wave rises falls unable uses fine grinding material wipe flat. Retreat back rough grinding working sequence. Anew pastes on 400 number silicon carbide sandpaper. Applies 3 kilograms/square centimeter uniform pressure crosses 45 degrees angle grinds damaged layer. Anew walks finish 600 number and 800 number sandpaper's process, consumed working hours increases three hours.

Polishing tools' soft hard degree towards heat amount transferring influence extremely big. Brass grinding rod transfers heat amount's speed is hard wood strip's three times. Hard wood strip friction produced heat amount far lower than high density wool felt. Uses soft flexible carrying handle cloth wheel cooperates 9 micrometers polishing paste forcibly presses dead corners, thirty seconds inside local hardness drops to 25 HRC.

Polishing liquid at friction interface's distribution state changed cutting trajectory. Every drop kerosene diluent added into polishing paste inside can carry away about 40 degrees Celsius surface heat amount. Under 3500 revolutions/minute's centrifugal force action kerosene in two seconds inside flings flies disappears. Dried up grinding material on hard particles slips and at leaning soft iron surface deep digs cuts.

Changes uses P20+Ni material's workpiece enters polishing table. 1% around nickel elevated full section hardness and changed iron chips' breaking off method. Applies 2 kilograms force way push grinds time cut down metal broken debris length only has 0.1 millimeters. Grinding disk surface not stuck iron chips, cutting path from beginning to end maintains clean.

Daily operation in obeying strict parameter limits can large margin reduce surface damage rate.

· Single time polishing operation time length full 20 minutes stop machine cools

· Grinding liquid and diamond paste according 1:3 ratio precisely formulates

· Hand-held grinding machine horizontal movement speed maintains per second 5 centimeters

· Every completes one grit number uses ultrasonic wave cleans surface residues

Uses high nickel content material processes. Experience abundant master dares takes polishing machine rotation speed towards up lift 200 revolutions. Nickel element brought full section toughness elevation lets surface bear polishing wheel per second dozens times impacts. Fine micro deformation by stuck in 0.002 millimeters inside. Light hits on light rays reflection trajectory neat orderly uniform one.

Facing complex shapes surfaces, polishing sandpaper's rough fine jumping must obey progressive ratio. From 800 number skipping levels jumps to 1500 number's span excessively big. Missing 1000 number and 1200 number's transition. Operator at 1500 number working sequence increased four times grinding time. Extra coming out friction heat lets wave rises falls under high temperature form shape.

Hardness testing instrument at normal P20 surface every separates 50 millimeters hits one Rockwell hardness point. Measured getting's data always at 28 to 32 between jumps moves. Polishing wheel walks past this 50 millimeters distance only needs 0.5 seconds. Cutting depth's changing amplitude high reaches 0.003 millimeters. Line of sight following light rays wanders walks, high low staggered wave broken faults clear visible.

Pitting

Polishing master gives steel board smears on 3 micrometers label's diamond paste, back and forth push grinds ten passes. Takes absolute ethanol takes surface's black oil wipes clean clean. Takes flashlight sticking steel board flatly shines past. Like mirror same's surface on popped out dozens 0.01 to 0.05 millimeters size pinholes.

Steelmaking factory's furnace burns to 1600 degrees, iron water tumbling time eats entered air inside's oxygen and brimstone. Steel water cools turned iron block, inside grew out hard hard aluminum oxide and manganese sulfide dregs. Conventional P20 steel board inside's sulfur content stays at 0.03% up down. Cuts open one square centimeter steel material, inside hides hundreds a few micrometers size dirty things.

Dregs particles compared surrounding iron flesh harder much, mutual between however sticks not tight. Grinding pad carries 1 micrometer size diamond broken dregs, by per second 8 meters speed scratches past steel board. Diamond edge produced pulling force exceeds 400 Megapascals. Crisp crisp manganese sulfide dregs receives not holds this burst strange force by pulled roots plucked up.

Dregs drop down, iron board on leaves behind one 0.02 millimeters deep sand hole. Plucked out hard particles not disappear, stuck in wool pad and steel board middle continuously rolls. One 0.05 millimeters size aluminum oxide broken debris can in three seconds inside, at just polished bright surface on plows out one stripe 20 millimeters long scratch.

Changes onto P20+Ni this piece material, steelmaking's formula completely changed routine. Factory takes iron water pumps into pressure not reaches 67 Pascals vacuum furnace inside discharges gas. This bout tossing about takes sulfur and phosphorus content dead dead presses in 0.005% this red line underneath. Steel block inside's non-metal dregs quantity one breath lacks 90%.

Takes same one piece wool pad goes pushes this piece contains nickel steel board. Machine opens to per minute 10000 revolutions goes sprint SPI A2 level's reflecting light degree. Steel board surface's roughness value steadily drops to 0.025 micrometers. Takes magnifying glass sticks close goes look, whole piece reflecting light surface on find not out half pin point big small pit.

Workshop inside has a set finds sand holes specific methods.

· Takes 100 times brings graduation lines small microscope measures pinhole has how wide

· Uses 1500 number sandpaper towards one direction follows pushes 5 minutes looks black points how run

· Calculates calculates 0.01% and 0.03% containing sulfur amount steel board falls off area differs how much

· Records down used drop how many grams 3 micrometers diamond paste and extra out how many sand holes' account

Two pieces steel boards deals with dregs falls off data placed on table surface on.

Fine sand paste cutting iron like mud's ability very weak, does one hour only can gnaw drop 0.001 millimeters iron skin. Original 0.02 millimeters deep sand holes edges corners by ground round, light rays one shine shadow area expanded one fold.

Old master will retreat back front three grinding steps. Anew pastes on one sheet new 400 number rough sandpaper. Changes uses cross crossing technique every time turns 45 degrees angle presses on 4 kilograms strength. Forcibly takes surface 0.03 millimeters thick damaged iron skin entirely scrapes drop, continuously grinds until microscope inside looks not see black points ends.

Grinding tools' soft hard degree influences dregs drops off. Takes density 0.8 grams per cubic centimeter cherry wood strip dips oleic acid does work. Wood receives squeezing takes diamond particles embed into wood fibers inside. Grinding material reveals out sharp corners goes cut, takes popping sharp dregs cuts flat not goes vividly pulls tears.

Pure cotton cloth wheel presses down goes will shrinks water 40%. Uses force against holds steel board time soft prone cloth strips wraps held a few micrometers size dregs particles. Four surroundings leaning soft iron flesh by cloth wheel dug empty, dregs foot bottom steps empty. Per minute two thousand times shaking follows trend takes shaking wanting to fall dregs shakes drops out steel board surface.

Surface emitting heat changed dregs surroundings loose tight degree. Polishing oil one dries local iron skin in ten seconds inside hot to 120 degrees. Iron skin receives heat expansion dimensions and crisp dregs fit not on beat. Microscopic level on staggered separated 0.005 micrometers gap, originally stuck held dregs follows loose moves.

Daily does work controls stops below these parameters can less out sand holes.

· Smears polishing paste thickness pressed in 0.1 millimeters inside

· Wool pad contacts steel board area do not exceed three parts of one

· Every separates thirty minutes drips three drops kerosene lowers temperature

· Polishing machine moves one meter spends drop time not less than twenty seconds

Stomach inside added nickel's P20+Ni in quenching after flesh quality very tight solid. Martensite grid takes micro small carbides particles wraps tight tight solid solid. Polishing wheel against 5 kilograms pressure at above horizontally sweeps. Carbides particles like tree roots same sticks in iron flesh inside, extremely hard drops off forms pit holes.

Buys normal P20 per kilogram saves down 2 bucks material money. Does good's mold pushes to last pass working sequence surface on bursts erupts out one big piece pinholes. Anew reworks grinds three passes, wasted drop sandpaper consumed drop diamond paste adding 48 hours wages, far far higher exceeds buys good material that little expense.

Pitfall Avoidance Guide

Buys back coming's P20 or P20+Ni steel board just onto polishing table, surface leaving milling machine walked past 0.05 millimeters deep cutter marks. Takes rough sandpaper opens rough is first pass gate limit. Skips pass 320 number sandpaper goes takes 400 number hard grinds, cutter marks bottom part metal tearing layer removes not drop. Left behind 0.01 millimeters dark injuries arrives exiting mirror surface time all turn into pockmarks.

Sandpaper grinding strength must pressed at per square centimeter 2.5 to 3 kilograms interval. Strength small eats not holds iron skin, strength big sand particles embed enters steel base body, pulls out is a pit.

Sandpaper number must according to 320, 400, 600, 800, 1000, 1200, 1500 order one sheet one sheet towards down pushes. Less walks one sheet 600 number, surface on leaves down 0.015 millimeters deep cross scratches. Following takes 800 number sandpaper extra grinds 40 minutes covers not hold. Friction time one long, surface temperature soars to 120 degrees, wave marks surely pop head.

Changes more fine label sandpaper, hand inside actions must turn a 45 degrees or 90 degrees direction. Following top one time's lines pushes, will take 0.02 millimeters wide scratches more digs more deep. Changes a push grinding direction, can clearly look clear top one pass sandpaper left behind marks have not have scraped clean.

Cleaning steps tolerates not gets half point steals lazy.

· Every changes one pass sandpaper uses absolute ethanol wipes area not less than 500 square centimeters iron board

· Uses ultrasonic wave cleaning machine shakes drop gaps inside 0.005 millimeters size grinding debris

· Changes number successively bringing changes new gloves and new wiping cloth

· Working table pad paper two hours changes one time prevents dust runs enters

Deals with normal P20, 15 micrometers diamond paste must pair brass rod. Brass compares iron softer a bit, can take diamond particles presses at surface 0.002 millimeters depth cuts. Uses soft wood strip goes battle, diamond at iron skin on slips, cuts not moves hard quality carbides.

Diamond paste usage amount absolutely not is smears more thick more good. One square centimeter steel board on point smears 0.05 grams paste body enough. Smears much grinding head floats at thick thick oil mud on slips. Friction surface temperature in 30 seconds inside shoots up to 140 degrees. Iron skin surface emits soft, wave rises falls following polishing wheel's trajectory one layer one layer piles up.

Same one 50 millimeters multiply 50 millimeters area, polishing wheel stays time absolutely cannot cross pass 3 minutes. Time one arrives immediately shifts position, lets emitting hot iron skin has 15 minutes natural drop temperature empty gap.

Pushes to 3 micrometers label's diamond paste, normal P20 and contains nickel material differences show appear. Normal P20 pushes on 5 minutes, meets sulfides impurities starts drops dregs outs sand holes. Bringing nickel steel board internal structure tight solid, can carry hold wool felt per minute 5000 revolutions high speed sweeps clears, continuously processes 15 minutes not out dregs.

Discovers iron skin on has wave rises falls or small sand eyes, absolutely cannot takes 1 micrometer fine paste goes fills pit. Fine material cutting force does one hour only enough scrapes drop 0.001 millimeters iron. Forcibly goes grinds will let sand holes edges collapse sink, area expands 3 times. Honestly honestly retreats back 800 number sandpaper, adds 4 kilograms press down force takes damaged flesh thickness thoroughly planes drop.

Electric polishing machine and hand works push grinding alternate has speaks究. Ultrasonic wave grinding machine set at per second 2 ten thousand times vibration frequency, deals with drop difference in 0.05 millimeters inside dead corners. Big area flat surface relies on two hands grips holding hard wood strip feels 2 kilograms press down feedback. Machine fixed dead at one point vibrates ten seconds clock, underneath iron flesh surely locally collapses sinks.