45 Steel Equivalent Grades | C45, S45C, EN8, 1045

Common equivalent grades for 45 steel include C45 (EN 10083), S45C (JIS G4051), EN8 (BS), and AISI 1045.

Its carbon content is typically around 0.42%–0.50%, with tensile strength of about 600–800 MPa.

It is commonly used in quenched-and-tempered condition, with a quenching temperature of 820–860°C and tempering at 550–650°C to improve overall performance.

C45

What does C45 mean?

The letter C indicates that this steel contains no costly alloy additions. The number 45 defines its carbon content. Inside the steelmaking furnace, the molten steel churns while the temperature gun reads 1,650°C.

The reading stabilizes at 0.46%, above the 0.42% lower limit and still slightly below the 0.50% upper limit. Workers add ferrosilicon and ferromanganese to the ladle to remove gas. The test sheet shows manganese at 0.65%, while silicon is held below 0.25%.

· Sulfur below 0.035%

· Phosphorus controlled within 0.030%

· Residual copper no more than 0.40%

An argon stirring lance is inserted into the molten steel for 15 to 20 minutes. The glowing steel is then cast into square billets, sent through a 1,150°C hot rolling mill, and repeatedly reduced before being drawn and cooled into cylindrical steel bars. A 15 mm thick sample is then cut.

The cut surface is polished to a mirror finish, etched with 4% nital, and examined under a metallographic microscope at 500× magnification. The field of view shows a black-and-white striped pattern. The white areas are soft ferrite, while the black stripes are hard cementite.

These two phases are interwoven in proportions corresponding to roughly 0.45% carbon. Under industrial standards, acceptable steel should have an internal grain size between Grades 5 and 8. The finer the grain, the greater the tensile load the material can withstand. The inspector clamps both ends of the round bar in a tensile tester, and the hydraulic system applies tens of tons of force.

The 50 mm gauge length gradually necks down. As the load approaches 600 MPa, the specimen breaks at the center with a dull snap. On the shop floor, cut 50 mm steel sections are stacked in piles. Baskets of gear blanks are pushed into a large bogie hearth resistance furnace set to 840°C.

Soaking time is calculated at 1.5 minutes per millimeter of section thickness. The red-hot parts are removed and plunged into circulating water at 20°C. A large cloud of steam erupts instantly. The cooling rate reaches hundreds of degrees per second, and the internal crystal structure changes dramatically.

A Rockwell hardness tester shows 55 HRC at the surface. A metal file dragged across the surface leaves no visible mark. Freshly quenched parts are as brittle as glass and can chip badly if dropped onto a concrete floor. They must be transferred to the tempering furnace immediately.

The furnace is set to 600°C for a full two-hour tempering cycle. The high temperature relieves the internal stress. The inspector then performs a destructive impact test.

· Pendulum weight: 30 kg

· Drop height: 1.5 m

· Impact energy at 20°C: 39 J

The fracture surface appears dark gray, rough, and fibrous. A heavy truck loaded with black round steel bars enters the machining shop. The delivery note states that one batch is supplied in the untreated condition. Another batch is marked as normalized at 860°C and air-cooled in the workshop. Surface hardness remains in the range of 160–210 HBW.

A flaw detector applies viscous couplant to the steel bars and scans the surface inch by inch with an ultrasonic probe. The green waveform on the screen remains stable. If the signal exceeds the alarm threshold equivalent to a 3 mm flat-bottom hole, the entire 6-meter bar is marked with a large red X.

Rejected material is returned to the electric arc furnace and remelted. Qualified material is clamped into the hydraulic chuck of a CNC lathe, ready to be machined into an automotive transmission shaft. The spindle is set to 1,200 rpm.

Mechanical Properties

The inspector takes a standard C45 test bar with a 10 mm diameter cross-section. Ambient temperature is controlled at 22°C. The upper and lower serrated grips of the universal testing machine clamp both ends firmly.

The hydraulic pump starts, and the machine pulls upward at 15 mm per minute. The load rises rapidly as the iron atoms inside the specimen are forced apart.

As the reading approaches 340 MPa, the pointer hesitates briefly and falls back slightly. At this point, the steel loses its spring-like ability to return to its original shape. On engineering drawings, this load is called the yield strength.

Once the load exceeds 340 MPa, the part undergoes permanent elongation. The machine continues to pull harder, and the reading climbs past 580 MPa.

The load then fluctuates between 600 and 700 MPa while the specimen visibly necks down in the middle. With a dull bang, the bar is torn in two. The maximum load sustained before fracture is recorded as the tensile strength.

The inspector fits the two broken halves together and measures the final length with a caliper. The original 50 mm gauge length has stretched to 58 mm. The elongation after fracture comes out to exactly 16%.

At the fracture location, the original 10 mm diameter has narrowed into a distinct waist. Measuring the thinnest section shows that the cross-sectional area has been reduced by a full 40%. The higher the reduction of area, the tougher the metal is and the less likely it is to shatter like glass.

A square C45 steel block, freshly cooled after normalizing, is placed on the test bench. The hardness tester uses a 10 mm tungsten carbide ball indenter.

A 3,000 kg load is applied. The ball is pressed heavily into the surface for 10 to 15 seconds. Once the indenter is removed, a distinct circular impression remains.

A measuring microscope is used to determine the indentation diameter. Comparing the result to the hardness chart on the wall shows that the larger the indentation, the softer the steel. C45 in the untreated condition usually measures between 160 and 210 HBW.

Now a blackened C45 part taken from the quench tank is tested. The hardness tester must be fitted with a sharp diamond cone indenter, and the load is reduced to 150 kg. The dial shows a Rockwell hardness as high as 55 HRC.

A 30 kg pendulum is hoisted by electric winch to a height of 1.5 m. A C45 square bar with a V-notch is mounted on the anvil below. The specimen dimensions are tightly controlled at 10 mm × 10 mm × 55 mm.

Once released, the pendulum slams into the back of the notched specimen. The bar breaks instantly and is thrown several meters away. The dial records the energy absorbed in fracture.

A C45 crankshaft model mounted on a fatigue tester spins at 3,000 rpm. A 50 kg iron weight hangs from the middle, applying a constant downward force.

As the crankshaft rotates, it is subjected to repeated bending stress. The machine runs through a full 10 million cycles before stopping. Not even a hairline crack appears on the surface.

A heavy stamping press in the factory uses a solid C45 cylindrical pin to secure the die. Two 50 mm thick steel plates apply a strong shear load from opposite directions. When the pin is finally sheared off, the force is roughly half of the tensile strength.

A stubby C45 cylinder 20 mm in diameter is placed under a 500-ton press. Two flat, ultra-hard steel plates compress it from above and below. The cylinder bulges outward and flattens into a disc.

A torsion tester clamps both ends of a long shaft. One end is fixed, while the other is twisted by a motor. The measured shear modulus remains consistently around 80 GPa, while the material’s elastic modulus stays fixed at 210 GPa.

Limitations

Whenever a welder picks up a C45 steel plate with 0.45% carbon, he tends to frown. Once the carbon equivalent value (CEV) exceeds the 0.40% threshold, the material becomes much more difficult under high-temperature arc welding. Molten weld metal at several thousand degrees causes the area around the weld to contract rapidly during cooling.

Microscopic cold cracks, invisible to the naked eye, can spread quietly through the heat-affected zone. An ultrasonic tester will show a chaotic pattern of defect echoes. To deal with the problems caused by high carbon content, the workpiece must be heavily preheated with an oxy-acetylene torch before welding begins.

The worker moves the torch back and forth over the joint area. The infrared thermometer must read above 150°C before arc ignition can begin. On heavy plate thicker than 20 mm, preheat temperature may need to exceed 250°C.

After welding, the part must never be left to cool in cold air. It must either be wrapped immediately in a heavy insulation blanket or placed in a 650°C annealing furnace for a full three hours to relieve the intense internal stress.

· Industrial power consumption for preheating and annealing increases several times over

· Labor standby time also increases significantly

· If cracking leads to scrap, the cost overrun can be severe

Beside the quench tank in the heat treatment shop lie several large round bars, each 80 mm in diameter. They are taken from an 840°C furnace and quickly plunged into circulating water at 20°C. A high-power saw then cuts them open, and the cross-section is etched with nital.

A bright white hardened layer appears near the outer circumference. A caliper shows the hardened depth has stalled at only 3 to 5 mm. Moving toward the center, the structure quickly changes back into dull pearlite.

The surface gives an excellent hardness reading of 55 HRC. But moving the probe inward, hardness drops sharply to around 25 HRC just 10 mm below the surface. Thick shafts end up with only a hard outer shell and a soft interior.

When solid material over 20 mm in diameter is water-quenched, the center simply cannot transform into martensite, so it cannot achieve high internal strength.

When designing a crusher main shaft weighing tens of tons, drawings can only specify 42CrMo alloy steel with chromium and molybdenum. Massive forgings hundreds of millimeters thick require costly alloying elements to harden all the way through. Plain carbon steel is no longer suitable.

At the open-air stockyard, several bundles of black steel bar delivered the previous day are sitting outside. It rained lightly overnight, and the relative humidity rose above 80%. By morning, a yellow-brown rust film has already formed on the gray-black surface.

A rough rag cannot wipe it away cleanly, and small corrosion pits have already begun to form. Since no chromium (Cr) or nickel (Ni) was added during steelmaking, rusting in the presence of moisture is an unavoidable fate for plain carbon steel.

· After machining, parts must be immersed in L-CKC grade anti-rust oil

· Before shipment, they may be electroplated with a 10 μm zinc coating

· They may also be black-oxidized in a 140°C sodium nitrite bath to form a black Fe₃O₄ film

Throw a test block into a deep cryogenic box filled with dry ice and alcohol, and the thermometer drops to -40°C. When struck in an impact tester, metal that could absorb 39 J at room temperature may shatter under only a few joules.

The fracture surface looks flat and glass-like, with no sign of plastic deformation. It must never be used for icebreaking shafts on polar research vessels operating in extreme cold. High-temperature service is equally problematic.

At boiler steam line joints, temperatures can remain around 450°C year-round. Ordinary carbon steel parts working under load in this environment may slowly elongate over time. Bolts that were originally tight may creep several millimeters after a few months.

Above 400°C, highly active carbon atoms move rapidly through the structure, and the once-stable metal lattice begins to deform and slip like softened plastic.

In workshops with strong magnetic fields, material selection for supports near MRI equipment is extremely strict. Bring a strong neodymium magnet close to a C45 steel plate, and it snaps onto the surface with a loud click. It cannot be pulled off by hand.

Inside a machine tool spindle sleeve, bearing balls may rub against the surface thousands of times per second. Even a quenched-and-tempered surface cannot withstand such extreme long-term friction indefinitely. After six months, a dial indicator may show journal wear beyond the 0.05 mm tolerance limit.

S45C

What does S45C mean?

The initial S comes from the English word Steel, indicating that the material is steel. The final C comes from Carbon, showing that carbon has been added during steelmaking.

The number 45 defines the target melt chemistry, requiring workers to keep the average carbon content at 0.45% as molten steel is poured. In practice, the actual value on the mill test report will never be exactly 0.45%. Inspectors accept only a narrow range from 0.42% to 0.48%. If it falls outside that range, the entire heat is rejected and remelted.

If carbon drops below 0.42%, ferrite becomes too dominant and behaves almost like dough against carbide cutting tools. Elongation before fracture may exceed 20%, and parts deform too easily. If carbon exceeds 0.48%, the pearlite content rises sharply, and the surface becomes prone to microscopic cracks during water quenching.

At 1,600°C, several bags of alloying additions are still charged into the furnace by weight. Workers add 0.60% to 0.90% manganese so the molten steel flows more smoothly into molds. Then they add 0.15% to 0.35% silicon to help remove gas before solidification.

The outgoing inspection rules set two absolute red lines. Phosphorus must not exceed 0.030%, and sulfur is capped at 0.035%.

If the lab finds phosphorus exceeding the limit by just 0.005%, the entire batch fails inspection. Strike that steel outdoors at -20°C and it may fracture instantly like ice.

Take a slice of freshly produced material, polish it, and observe it at 500× magnification. Two contrasting structures appear: the white phase is ferrite and measures only about 80 HB, while the darker pearlite is harder and can reach about 200 HB.

This soft-hard mixed structure makes machining easier. A machinist sets the spindle to 800 rpm and the feed to 0.2 mm per revolution. The chips fall in neat spiral curls. A low-cost tungsten carbide insert can finish 300 shafts in a row without replacement.

Common stock forms produced by the mill include:

· Black round bar from 10 mm to 250 mm in diameter

· Square plate from 10 mm to 150 mm in thickness

· Hexagonal bar with width across flats from 12 mm to 65 mm

· Pickled wire rod in coils at 5 mm diameter

Rough stock with mill scale typically contains around 150 MPa of residual stress. Workers place it in an 850°C gas-fired furnace for two hours, then let it cool slowly inside the furnace to 500°C before removal. After this, hardness drops back to around 167–229 HB.

A flatbed truck delivers 6-meter round bars to the machining shop, where the first operation is done on a large band saw. Cutting through a 50 mm bar takes about two minutes with a bi-metal blade. A caliper shows that height variation at the cut face is less than 0.5 mm.

After turning, the part is sent to a high-frequency induction line. After just two seconds of heating, the metal surface reaches 860°C. Coolant is sprayed immediately, hardening the outer layer to a depth of 1.5 to 3 mm. A file dragged across the surface confirms a hardness of 45 to 50 HRC.

Hardware manufacturers across the Yangtze River Delta consume hundreds of tons of this material every day to produce all kinds of components:

· Spur gears with 30 to 80 teeth for gearboxes

· 150 mm miniature motor shafts for household appliances

· Hydraulic cylinder cap sleeves تحملing 10 tons of oil pressure

· M16 Grade 8.8 bolts used on stamping press bases

Compare it against low-carbon mild steel containing 0.20% carbon. If cylindrical test bars with the same 1 cm² cross-sectional area are pulled in tension, this material resists until the load reaches about 3.5 tons. When the dial reaches 569 MPa, the specimen breaks with a sharp bang.

It is highly vulnerable to moisture and offers very limited rust resistance. During the rainy season in southern China, warehouse humidity exceeds 80%. Leave the bars on muddy ground for two days, and yellow-brown rust appears on the surface. Storekeepers have to brush them with anti-rust oil every week and wrap them in three layers of waterproof plastic.

When scrap is remelted and a new heat is tapped, the lab prints a barcode-tagged inspection sheet. It lists the actual spectrometer readings for C, Si, Mn, P, and S, accurate to three decimal places. The certificate is shipped together with 50-ton bundles to machinery plants across the country.

Replacement with 45 Steel and 1045

A factory receives a foreign-language drawing specifying S45C. The buyer goes to the steel market, where the supplier offers stock labeled simply as 45 steel. A 3D model sent by an American customer lists 1045 in the material field. The workshop foreman checks the 50 mm black round bar at hand with a caliper and tells the operator to cut it on the large band saw.

Spark emission spectrometer tests show strikingly similar chemistry. Under China’s GB/T 699 standard, 45 steel contains 0.42% to 0.50% carbon. Under ASTM A29, 1045 steel contains 0.43% to 0.50%. Under JIS, the range is 0.42% to 0.48%. The maximum difference in carbon range is only 0.08%.

The American and Japanese standards raise the lower manganese limit to 0.60%, while Chinese 45 steel qualifies at 0.50%. That 0.10% difference in manganese can affect hardenability during water quenching. The ASTM grade does not specify a fixed silicon value, so steel mills usually add about 0.10% to 0.20% as a deoxidizer.

ASTM permits up to 0.050% sulfur and 0.040% phosphorus. China limits both to 0.035%, while the Japanese standard is stricter on phosphorus, rejecting material above 0.030%. Reducing impurities by 0.010% can lower cold brittle fracture rates in crane gears operating at -10°C by roughly 15%.

When these three materials are heat-treated at 840°C and tempered at 600°C, their tensile curves almost overlap. A universal testing machine pulls specimens with a 150 mm² cross-section to failure. Yield strength stays around 355 MPa, and tensile strength remains in the range of 600 to 650 MPa.

In the Wuxi steel market, domestically produced 60 mm hot-rolled round bar is listed at RMB 4,200 per ton. If the buyer insists on original imported S45C with customs documentation, freight and duty add another RMB 1,800 per ton. For an order of 50,000 agricultural transmission shafts, that creates a raw material cost difference of RMB 90,000.

A hydraulic valve block used in Boeing aircraft landing gear may be stamped 1045 on the drawing. Foreign inspectors check a 10 mm thick material certificate line by line. If Chinese domestic material is substituted, an entire batch of 3,000 precision valve blocks may be scrapped on the spot. In aerospace and defense applications, even a 0.05% impurity-related reduction in fatigue life is unacceptable.

For steel tubes 28 mm in diameter that are cut at a rate of 100,000 pieces per day, with wall thickness as low as 2 mm, workers focus only on whether induction hardening for three seconds can achieve 40 HRC. If the steel ball on the hardness tester leaves no indentation, the entire batch is loaded and sent to a furniture assembly plant without anyone caring which national standard it originally came from.

When sales staff quote against foreign material specifications, they often calculate unit cost using domestic material plus a 5% loss allowance. A third-party agency takes a 50 g remnant sample for spark spectrometry. If carbon measures 0.46% and impurities are within spec, a compliant test report is enough to secure customs clearance before the vessel departs.

Experienced drill operators can often sense the material difference by feel. With a 12 mm twist drill running at 500 rpm, ASTM material with slightly higher sulfur produces short, breakable chips and can often be drilled without coolant. Chinese standard material tends to produce continuous spiral chips up to 15 cm long. Operators must tap the brake to break the chip and avoid cuts through their canvas gloves.

When turning bars stamped with imported markings, insert wear may vary subtly. Removing 3 mm from the outer diameter of domestic bar, the insert usually needs to be flipped after about 200 pieces. With genuine JIS round bar, the same insert can often finish 230 pieces while still maintaining a 1.6 surface finish. At the end of the month, the shop records these tooling differences precisely in the production cost report.

EN8

Three Advantages

When machining EN8, lathe operators typically use coated carbide inserts. Cutting speed is set to 120–150 m/min, with feed fixed at 0.2–0.3 mm per revolution. The chips curl away in standard C-shaped fragments. The spindle motor load meter stays at about 70% of what it would show when machining chromium-molybdenum alloy steel.

A single VNMG160408 insert can cut continuously for eight hours. Measuring flank wear with a caliper shows only 0.15 mm of wear. Because inserts do not need to be changed frequently, the average daily utilization of a CNC machine stays above 85%. If an ordinary high-speed steel drill is used at 25 m/min, the drilled surface feels smooth to the touch, and a roughness tester consistently reads Ra 3.2 μm.

At the vertical milling machine, the operator switches to a 63 mm four-flute face mill. Depth of cut is set to 3 mm and spindle speed to 800 rpm. The falling chips show a faint bluish tint. For thread turning, a PVD-coated insert is used at 90 m/min. The finished thread profile is full and clean, with no built-up edge at the tool tip.

A Go/No-Go M12 thread gauge screws smoothly into 99 out of 100 blind holes just tapped. In the corner of the workshop, a wire EDM machine is cutting 100 mm thick steel plate, with the molybdenum wire moving back and forth through the dielectric fluid at 80 mm² per hour.

On the induction hardening line, a pure copper water-cooled coil surrounds the outer diameter of a shaft. Frequency is set at 30–50 kHz. After two seconds of heating, the outer ring turns red-hot, and cooling water is sprayed immediately. Surface hardness at a depth of 1.5–2.0 mm reaches HRC 50–55.

Cut the hardened shaft open and test the core with a Brinell hardness tester: the reading stays around 200 HB. Blank parts are pushed into a crawler-type furnace set between 830°C and 860°C for full heating. Once fully soaked, they are removed and quenched in a polymer solution, allowing hard martensitic structures to form rapidly at the surface.

· Water quench from 850°C, followed by tempering at 550°C

· Oil quench from 840°C to reduce distortion in slender shafts

· Oxy-acetylene flame hardening on large gear surfaces

· Nitriding in an ammonia furnace at 500°C to improve surface wear resistance

· Slow cooling in an electric furnace at 600°C to relieve residual stress

Transmission half-shafts installed in vehicle chassis are subjected to thousands of N·m of torque year after year. With tensile strength of 500–800 MPa, the material can withstand this destructive load without fracture. The purchase price is also attractive. Buying one ton of this material costs nearly 30% less than buying the same weight of 42CrMo4 alloy steel.

Agricultural machinery plants use it in large quantities for splined shafts. Large pulley blanks for heavy conveyors are heated in a natural gas forging furnace to 1,150°C until they become as soft as dough. A gravity air hammer then strikes 200 blows per minute, forging 100 mm square billets into solid round bars.

The hot forged bars are pushed into a pit for slow cooling, where the temperature remains around 300°C to prevent internal microcracking. A cut sample observed under a metallographic microscope at 500× shows the familiar black-and-white striped structure. Harmful sulfur and phosphorus impurities are both kept below 0.05%.

· Involute spur gears with module 4

· Motor main shafts turned to an outer diameter of 45 mm

· M24 high-strength bolts used to clamp large flanges

· Trapezoidal lead screws up to 1,200 mm long

· Crank connecting pins carrying a vertical load of 20 kN

The machine screen shows yield strength consistently above 275 MPa. A standard specimen after quenching and tempering is mounted in a fatigue tester and rotated through 10^7 cycles without fatigue fracture. The measured modulus of elasticity stays clearly within 200–210 GPa.

On a precision surface grinder, a new white alumina wheel is installed and run at 35 m/s. The table feed is advanced by 0.01 mm each pass. The final surface variation is less than 0.005 mm. A heavy drawing machine pulls a 20 mm round bar through an 18 mm alloy die, compressing the outer surface into a dense hardened shell.

The cold-drawn bar is then tested, and yield strength jumps to 460 MPa. It is cut into precision smooth shafts for 3D printer linear guides. The parts are sent to the electroplating shop for hard chrome plating; before entering the bath, they are cleaned in an acidic solution for three minutes to remove mill scale. The plated surface achieves a bond strength of 15 MPa.

The CNC lathe operator enters a G71 rough turning cycle and sets the depth of cut to 2.5 mm per pass. The hydraulic three-jaw chuck applies 4 MPa of clamping pressure, holding the part firmly without leaving clamping marks. At the coordinate measuring machine in the temperature-controlled room, a ruby probe scans the part, and the system calculates cylindricity error at just 0.012 mm.

Precautions

Before striking an arc, welders usually check the temperature of the EN8 workpiece by hand. Once carbon exceeds the 0.36% threshold, the sudden heat of arc welding can create hard and brittle structures around the weld. If it is welded the same way as Q235 mild steel, visible cracks may appear around the weld after cooling.

An infrared heater is moved into place, and the area within 100 mm around the weld is preheated to 150°C–250°C. Once the infrared thermometer confirms the temperature, the worker switches to E7018 low-hydrogen electrodes. During multi-pass welding, temperature crayons are used continuously to keep interpass temperature below 300°C.

The welding machine current is set to 120–140 A, and the operator runs a steady bead using a 3.2 mm electrode. As soon as welding ends, the workpiece is wrapped tightly in an insulation blanket. It must cool slowly over 4 to 6 hours so the internal grains have enough time to stabilize.

For heavy flanges over 30 mm thick, blankets are not enough. A forklift carries the flange into a bogie hearth furnace set to 600°C–650°C. It is held for two hours and then cooled slowly in the furnace down to 200°C before removal, fully relieving welding stress.

If exposed to air for less than 24 hours, moisture can already produce a yellow-brown rust film. Bare EN8 has virtually no oxidation resistance. If stored in a warehouse with humidity above 60%, more than half the surface may rust within three days.

The cheapest anti-rust treatment is black oxide. Parts are immersed in a boiling alkaline blackening bath heated to 135°C–145°C for 20 minutes. This forms a 0.5–1.5 μm black Fe₃O₄ film on the surface. After immersion in anti-rust oil and drying, the parts can pass a 48-hour salt spray test.

For export shipments, customs inspection is stricter on surface treatment. Small parts are loaded into electroplating barrels and coated with an 8–12 μm blue-white zinc layer. After 96 hours in a neutral salt spray chamber, the surface may show only slight white rust, with no red rust at all.

Large reducer housings up to 3 meters long cannot be immersed in a tank. Painters spray an epoxy zinc-rich primer evenly over the steel plate. Dry film thickness reaches 60 μm, followed by a 40 μm polyurethane topcoat. Cross-hatch adhesion testing gives Grade 1, and the coating can withstand five years of outdoor weathering without peeling.

Before stepping on the press brake pedal, the operator measures sheet thickness carefully with a caliper. When bending a 5 mm cold-rolled plate, if the inside bend radius is less than 10 mm, the outer surface experiences extreme tension and may burst with fine network cracks.

Its resistance to deformation is roughly twice that of ordinary steel plate. In cold-heading machines making M16 high-strength hex bolts, the incoming wire rod must first undergo spheroidizing annealing at 720°C. Hardness falls below 170 HB, allowing the die to strike 80 times per minute and form smooth hex heads with no cracks at the edges.

A gantry milling machine removes 20 mm of stock from a steel plate in one pass. Once that much material is removed, the internal stress state becomes severely unbalanced. A 2-meter machine guide rail blank may spring upward by 1.5 mm at both ends as soon as the clamping plates are released. Any part that loses 30% of its original volume through machining must be treated accordingly.

1045

Chemical Composition Limits

At the steelmaking furnace, the thermometer points to 1,600°C while the inspector watches the screen for a carbon content of 0.43% to 0.50%. If a quenched workpiece is taken from the brine tank and tested, and the carbon content has fallen to 0.41%, the hardness reading will reach only about 38 HRC at best.

If carbon crosses the 0.50% upper limit, the material may fail before even reaching 16% elongation in a room-temperature tensile test. A machinist running overly high-carbon stock on the lathe may find that an insert that once turned 50 shafts now wears out in fewer than 25.

Silicon-manganese alloy is added to the melt to bring manganese into the range of 0.60% to 0.90%. If the lab report shows only 0.50% manganese, hardness drops sharply less than 3 mm below the surface on a cut cross-section.

Adding just a little more manganese has an immediate effect on the internal behavior of the material:

· Raises matrix yield strength by about 30 MPa

· Ties up free sulfur into manganese sulfide

· Delays the critical quenching cooling rate by about 15%

· Suppresses excessive austenite grain growth at 1,000°C

Sulfur is held below 0.050% on the scrap report. When a 1,000°C rolling mill reduces ingots into 100 mm plate, excessive sulfur causes torn, jagged edges. Some processors deliberately order free-machining steel bars with sulfur controlled near 0.045%.

Under high-speed cutting, small inclusions help break long chips into short segments, allowing each machine to produce 20 more flanges per hour. The lab limit for phosphorus is 0.040%, but large mills usually keep outgoing material below 0.025%.

When the temperature drops to -20°C, striking a scrap round bar containing 0.060% phosphorus with a sledgehammer produces a crystalline fracture surface with no sign of ductility. To prevent this, steelmakers impose strict controls:

· Use double-slag refining to keep phosphorus and sulfur below 0.015%

· Every 0.01% increase in phosphorus reduces impact energy by 8 J

· Prevent inclusions above Grade 2.5 from interfering with ultrasonic inspection

Silicon is specified in the domestic standard at 0.17%–0.37%, and about 1.5 kg of ferrosilicon is added per heat to remove oxygen. Residual chromium, nickel, and copper from scrap are still acceptable as long as each stays below 0.25%.

If the bar contains 0.15% chromium, rusting may be delayed by two full days even when the material is left on damp ground in the workshop. On a 120-ton continuous caster, the outer area of the solidified strand may show 0.44% carbon by spectrometer.

Probe toward the center of the round section and the value may jump to 0.49%. If the carbon variation across three test points on the end face of a 200 mm bar exceeds 0.03%, the entire 60-ton heat may be downgraded.

Mechanical Properties

In the workshop, the universal testing machine grips an as-rolled 1045 round bar specimen. The hydraulic cylinder begins to pull upward slowly. As the dial passes 310 MPa, slight necking appears in the middle of the specimen, and the material permanently loses its elastic recovery.

The hydraulic cylinder continues to load the specimen until the reading climbs to around 600 MPa. With a dull snap, the 20 mm test bar fractures. The inspector measures the broken specimen with a caliper: the original 100 mm gauge length has extended by 16 mm, giving an elongation of exactly 16%.

On the inspection bench sits a Brinell hardness tester with a 10 mm tungsten carbide ball indenter. Under a 3,000 kg load, an untreated 1045 steel block forms a shallow indentation. Based on the measured diameter and the hardness chart, the result typically falls in the range of 163–207 HB.

After normalizing at 850°C and allowing the part to air-cool on the shop floor, the originally irregular ferrite grains become finer and more uniform, and yield strength quietly rises to 340 MPa.

The process that truly transforms this steel happens by the quench tank. The furnace thermometer reads 840°C. A glowing red shaft is hoisted out and plunged into circulating water. In less than five seconds, the internal structure completes its transformation to martensite.

Fresh from the water, the part is as brittle as glass and may crack if dropped on concrete. Workers immediately place it in a 600°C tempering furnace for two hours. After this treatment, tensile strength rises sharply to 800 MPa, while yield strength stabilizes at 490 MPa.

A test block with a 2 mm deep V-notch at the center is broken by a 300 J pendulum. The energy absorbed in fracture is 39 J. In winter, under subzero conditions, impact energy on the same batch may drop to around 25 J.

Some gears require a wear-resistant surface but a tough core. An induction coil is placed around the gear, and high-frequency current heats the surface to the quenching temperature before water spray cooling. Surface hardness immediately jumps to 50 HRC, but a sectioned test shows the core remains only about 25 HRC at 1.5 mm below the surface.

To make workshop reference easier, the technical department posts a table of measured mechanical properties for different conditions:

If a press crankshaft is made from untreated hot-rolled stock, alternating stress above 300 MPa may bend it within a month of operation. Switching to quenched-and-tempered material increases bending resistance by nearly 200 MPa.

Senior engineers rarely specify a single rigid value on drawings. For quenched-and-tempered hardness, they usually call out a range such as 25–28 HRC, leaving the heat treatment operator a process window of about 3 HRC. In a load of 200 parts, those near the furnace wall may heat faster and reach 28 HRC, while parts packed in the middle may measure only 23 HRC.

A torsion tester clamps both ends of a 25 mm transmission shaft and applies opposite torque. Once the dial exceeds 450 N·m, fine diagonal slip lines appear on the shaft surface. Untreated bar may break apart once the twist angle exceeds 45°, while quenched-and-tempered material can endure up to 80° before obvious tearing appears.

In the fatigue lab, machines run through the night, using an eccentric mechanism to simulate tens of millions of high-frequency load cycles. The quenched-and-tempered specimen withstands fully reversed stress through 10^7 cycles, leaving only shell-like fatigue propagation marks on the fracture surface.

In one corner of the shop, annealed material is kept for cold-heading machines. After being held at 750°C for four hours, Brinell hardness drops to about 150 HB. Under hundreds of tons of forging pressure, the round bar deforms like dough into a hex bolt head without any visible cracking.

Machining and Forming

Machinists like working with 1045 on the lathe. A standard CNC lathe grips a 50 mm round bar and runs at 800 rpm. A carbide insert engages the metal at 0.2 mm/rev feed, and pale blue chips fall cleanly through the chip conveyor.

Its machinability rating is about 57%, based on 1112 free-machining steel as 100%. Chips do not wrap around the chuck like chewing gum. Instead, they curl naturally into small C-shaped springs and break away. A standard coated insert can cut continuously for about 45 minutes before it needs to be indexed.

On the milling machine, spindle speed is reduced to 400 rpm. An 80 mm face mill sweeps across the blank while emulsion coolant diluted at 1:15 is sprayed continuously. Cutting temperature is held below 200°C, and the milled surface easily falls within an Ra 3.2 roughness requirement.

Drilling is very demanding in terms of chip evacuation. In blind holes with a depth-to-diameter ratio greater than 5, the drill should be retracted every 8 mm of depth. If forced deeper without clearing chips, coolant cannot reach the cutting edge, and the drill tip may overheat to 600°C, soften, and turn blue.

The flames in the heating furnace lick across square steel billets while the temperature holds at 1,200°C. Wearing heavy canvas gloves, workers use long tongs to pull out the bright yellow-hot steel and drop it into the lower die of a 1,000-ton friction press.

The massive ram comes down with a deafening roar. A 200 mm billet is instantly compressed into a rough gear shape, while scale flies off and hits the floor with faint white smoke. The entire forging process must be completed before the workpiece cools below 820°C.

Once the surface color darkens from bright yellow to cherry red, deformation resistance rises three to four times. If the operator keeps striking it anyway, the edges may tear open with 2 to 3 mm deep cracks. Freshly forged hot parts must never be quenched in water.

The red-hot forging should be placed in dry sand and covered with an insulating blanket. If it is left on a 5°C concrete floor instead, the temperature difference of several hundred degrees can tear the internal structure apart, and ultrasonic inspection will show dense crack signals.

If 1045 round bar is drawn through a die without prior annealing, the drawing force may instantly exceed machine limits. Even a 10% reduction in diameter can leave fish-scale cracks all over the surface, and the tungsten carbide die may be worn out after just two tons of material.

If the material is annealed at 750°C for four hours and then cooled slowly with the furnace down to 500°C, Brinell hardness drops to about 150 HB and the material softens considerably. It can then be fed into a cold-heading machine, where a punch applying hundreds of tons of force can upset a 20 mm bar into a hex bolt head.

· For punching and blanking, single-side die clearance should be about 8% of sheet thickness

· When shearing 10 mm plate, blade clearance should be widened to 0.8 mm

· If the bend radius of tubing is less than 1.5 times the tube diameter, the outer wall is likely to tear

· Before tapping, the pilot hole should be enlarged by 0.1 mm compared with mild steel to reduce the risk of tap breakage

When tapping M12 threads in annealed material, the tap should reverse half a turn after every two forward turns to break the chips. If the material has already been quenched and tempered to 28 HRC, cutting oil must be applied continuously, and once speed exceeds 15 rpm, even a cobalt tap may snap off inside the hole.

Grinding wheel speed is set to 35 m/s, with a very light infeed of 0.01 mm. Sparks are sparse, and coolant washes away residual heat. The finished piston rod surface reflects like a mirror, and micrometer measurement shows cylindricity error below 5 μm.