65Mn Spring Steel-SCALE STEEL.
65Mn spring steel, manganese to improve hardenability, φ12mm steel can be quenched in oil, surface decarburization tendency is smaller than silicon steel, after heat treatment of the comprehensive mechanical property is better[SCALE STEEL] than carbon steel, but has overheating sensitivity and temper brittleness. It can be used as small size flat, round spring, cushion spring, spring spring, spring ring, valve spring, clutch spring, brake spring and cold drawn wire cold coil coil spring, etc.
Execution standard: GB/T 1222-2007
● Characteristics and scope of application:
65mn strength. Hardness, elasticity and hardenability are higher than No. 65 steel, with overheating sensitivity and tempering brittleness tendency, water quenching has the tendency to crack formation. Annealed state machinability [SCALE STEEL]is acceptable, cold deformation plasticity is low, poor weldability. Plate springs under moderate load, helical springs and spring washers up to 7-20mm in diameter. Spring ring. High wear resistance parts, such as grinder spindle. Spring clamp. Precision machine tool screw. Cutting tools. Sleeve rings for spiral roller bearings. Railway rails, etc
● Chemical composition(%):
Carbon C: 0.62 ~ 0.70 Si: 0.17 ~ 0.37
Manganese Mn: 0.90 ~ 1.20[SCALE STEEL]
Sulfur S: ≤0.035
Chromium Cr: ≤0.25
Nickel Ni: ≤0.30
Copper Cu: ≤0.25
● Mechanical Properties:
Tensile strength σb (MPa) : 825~925
Elongation δ10 (%) : 14~22.5
Reduction rate of cross-section (%) : no more than 10
Hardness: hot rolling,≤302HB; Hot rolling + heat treatment,≤321HB
● Heat Treatment Specification and Metallographic Structure:
Heat treatment specification: [SCALE STEEL]quenching 830℃±20℃, oil cold; Temper 540℃±50℃(for special needs,±30℃).
Metallographic Structure: Tretinite.
● Critical point temperature (approximate value) Ac1=726℃, Ac3=765℃, Ar3=741℃, Ar1=689℃, Ms=270℃.
Normalizing specification: temperature 810±10℃, air cooling. 
● State of delivery: hot[SCALE STEEL] rolled steel to heat treatment or no heat treatment of delivery, cold drawn steel to heat treatment of delivery.
● Supply specifications:
Disk circle: Φ5.5 ~ 16mm
Forging: Φ160 ~ 450mm
65Mn density ρ= 7.85g/cc, the steel can be cold rolled into steel plate, steel strip and steel wire, the production of spring. 65Mn can also be made into tools such as fitter's chisel, cutting needle, etc. 65Mn steel can be made of general section size of 8 ~ 15mm or so small spring, such as a variety of small size flat, round [SCALE STEEL]spring, cushion spring, spring spring.
760℃×30min insulation, and then at 20℃/h cooling rate to 700℃×6h furnace cooling, to obtain a complete spheroidized structure, uniform size.
Argon arc welding butt welding process
In order to reduce the consumption of electrodes, DC positive connection is selected for wire butt welding test, that is, DC power supply is selected, the wire is connected to the positive pole of the power supply, and the tungsten pole is connected to the negative pole of the power supply.
The tungsten electrode containing 1% or 2% thorium oxide has high electron emission efficiency, good current carrying capacity, good anti-pollution performance, easy arc starting and stable arc. For ease of handling, a thinner thorium tungsten electrode with a diameter of 2 mm was selected and the front end of the electrode was sharpened.
Argon is chosen as the protective gas because of its low arc voltage characteristic, which is especially useful for manual arc welding of thin sheet and wire.
Dc manual argon arc welding machine was selected for the test. Before welding, the two ends of the wire were carefully smoothed.[SCALE STEEL] In order to prevent the porosity of the welding spot, the oil at the end was cleaned with acetone. Place the polished wire at both ends on the flat and clean aligning plate (Figure 1), so that the two ends are aligning, leaving no gap at the joint, and press both sides of the joint with a pressing iron. Connect the wire to the positive electrode of the welder and the tungsten electrode to the negative electrode, and then switch the current to 20 A, 15 A, 10 A and 8 A respectively for welding. When welding, the ignition point arc next to the joint and make it burning stable, the arc moved to the joint to melt the joint metal and quickly extinguish the arc, at the same time,[SCALE STEEL] slightly apply the top forging force, after cooling to complete the welding process, the welding process does not use filler wire.
It is found that when the welding current is 20 A, the arc combustion is intense, the metal spatter at the joint is serious, and the solder joint collapse is serious. When the current is adjusted to 15 A, the arc combustion is stable and the pool spatter is less, but the weld is still collapsed. However, when the current drops to 10 A, arc initiation is easy, arc combustion is stable, and there is no collapse phenomenon at the weld. Figure 2 shows the shape of the welded joint photographed with A digital camera under Leica MZ6 stereo microscope at a welding current of 10 A. It can be seen that the cylindricity of the joint is good, and it can meet the requirements of the line saw after grinding. When the current is adjusted below 8 A, it is difficult to start the arc and the arc is unstable, so it is difficult to complete the welding process.
Welded joint test
Due to the tendency of 65Mn steel to overheat, the welding heat affected zone has great influence on the mechanical properties of the joint. The joint of 65Mn steel wire with diameter of 0.7mm is very hard and brittle after argon arc welding. If the welding spot is gently bent, it will be brittle at the fusion line or weld, and the fracture shows obvious brittle fracture morphology. The obtained joint consists of a weld and a heat-affected zone, and the microhardness of each zone from the weld center to the base metal is tested along the joint axis. The measurement results show that from the base metal to the heat-affected zone and the middle of the weld, the microhardness increases sharply, and the hardness in the middle of the weld reaches HV 1 060, which indicates that hard and brittle structures are formed in the heat-affected zone and the middle of the weld. For this kind of joint with hard and brittle structure, in order to improve its toughness and plasticity, reduce its hardness, hardness, strength, plasticity and toughness of the appropriate match, must be the welding joint for appropriate tempering treatment. After heat treatment, the brittleness of the heat affected zone should be eliminated, while the base material should be able to maintain a certain strength and elasticity. Tempering is carried out in the box-type resistance furnace, and the tempering process is shown in Table 1. The tempered steel wire welding joint is carefully polished so that its diameter is roughly equal to that of the base material, and then the tensile test is carried out on the WE-50 tensile testing machine. Take three samples of each tempering treatment, and take the average value of their tension.
It can be seen from the test that after heat treatment above 330℃, the elasticity of the base material basically disappears, and the fractures all occur in the base material, rather than in the solder joint and its heat-affected zone, which indicates that although the brittleness of the heat-affected zone disappears completely after heat treatment, the strength of the base material is greatly reduced (the tensile strength of the base material used is 1 663 MPa after the test). At 260℃ for 10 min, although the elasticity of the material is basically unchanged, the brittleness of the heat affected zone cannot be eliminated. When the heating temperature is 280℃ and the heat is held for 10 min, the effect is the best. The tensile strength of the heat affected zone is only about 20% lower than that of the base material, and the elasticity of the base material is less disappeared. The microhardness of the welding head tempered at 280℃ was tested along the axis in each zone of the longitudinal profile. It was found that the maximum hardness value of the weld was reduced to about HV 500, which was about 1 times lower than that of the untreated one. Welded ring wire should not only meet the requirements of strength and elasticity, but also have a certain fatigue strength.
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