65Mn Steel Plates

65Mn Steel Plates

65Mn steel plate, manganese to improve the hardenability, φ12mm steel oil can be quenched through, the surface decarburization tendency is smaller than silicon steel, the comprehensive mechanical properties after heat treatment is better than carbon steel, but there is overheating sensitivity and temper brittleness. Used as a small size of various flat, round spring, cushion spring, spring spring, can also make spring ring, valve spring, clutch spring, brake spring and cold drawn wire cold coil spring.

Basic information

Chinese name:65Mn steel plate

Yield strength σs:≥784(80)(MPa)

Elongation δ10:8 or higher (%)

Shrinkage of section:Acuity 30 (%)

Standard

65Mn steel plate introduction

Standard :GB/T 711-88 137 0210 4496

use

65Mn steel plate strength, hardness, elasticity and hardenability are higher than 65 steel, with overheating sensitivity and tempering brittleness tendency, water quenching has a tendency to crack. The machinability of annealed state is reasonable, the cold deformation plasticity is low, and the weldability is poor. Moderately loaded plate springs, coil springs with a diameter of 7-20mm and spring washers. Spring ring. High wear resistance parts, such as grinding machine spindle, spring clamp, precision machine tool screw, cutter, spiral roller bearing sleeve ring, railway rail, etc.

Chemical composition

Carbon C :0.62~0.70

Silicon Si:0.17~0.37

Manganese Mn:0.90~1.20

Sulfur S :≤0.035

P :≤0.035

Chromium Cr:≤0.25

Nickel Ni:≤0.30

Copper Cu:≤0.25

Folding mechanical properties

Tensile strength σb (MPa):≥980(100)

Hardness: hot rolling,≤302HB; Cold drawing + heat treatment, ≤321HB

Folding heat treatment specification and metallographic structure

Heat treatment specification: quench 830℃±20℃, oil cold; Temper 540 ° C ±50 ° C (for special needs,±30 ° C).

Metallographic structure: troostite.

● Delivery status: Hot rolled steel is delivered in heat treatment or no heat treatment state, cold drawn steel is delivered in heat treatment state

weldability

Folding argon arc welding butt welding process

In order to reduce the consumption of the electrode, the DC positive connection is selected for wire butt welding test, that is, the DC power supply is selected, the wire is connected to the positive electrode of the power supply, and the tungsten electrode is connected to the negative electrode of the power supply.

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 operation, a thinner thorium tungsten electrode with a diameter of 2 mm is selected, and the electrode front end is sharpened.

Argon is chosen as the shielding gas because of its low arc voltage characteristic, which is particularly useful for manual arc welding of thin sheet and wire.

Dc manual argon arc welding machine was used in the test. Before welding, the two ends of the steel wire were carefully smoothed. In order to prevent porosity in the welding joints, the oil at the ends was cleaned with acetone. Place the two ends of the polished wire on the flat and clean alignment plate (Figure 1), so that the two ends are aligned, without leaving a gap at the joint, and press the two sides of the joint with a press iron. Connect the positive electrode of the wire welding machine and the tungsten electrode to the negative electrode, and switch the current to 20A, 15A, 10A, 8A respectively for welding. When welding, the ignition arc next to the joint is made stable, the arc is moved to the joint to melt the joint metal and the arc is quickly extinguished, and the overforging force is slightly applied, and the welding process is completed after cooling, and the filler wire is not used in the welding process.

It is found that when the welding current is 20 A, the arc burning 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 more stable, the pool splash is less, but the weld is still collapsed. However, when the current is reduced to 10 A, it is easy to initiate arc, arc combustion is stable, and there is no collapse phenomenon at the weld. Figure 2 shows the shape of the welded joint taken by A digital camera under a 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, the arc is difficult to start and the arc is unstable, and it is difficult to complete the welding process.

Folding welded joint test

Due to the tendency of 65Mn steel to overheat, the welding heat affected zone has a great influence on the mechanical properties of the joint. The 0.7mm diameter 65Mn steel wire is very hard and brittle at the joint after argon arc welding. If the solder joint is slightly bent, it will be brittle at the fusion line or weld, and the fracture will show obvious brittle fracture morphology. The resulting joint consists of a weld and a heat-affected zone, and the microhardness of each zone from the weld center to the base material is tested along the joint axis. The measurement results show that the microhardness increases sharply from the base material to the heat affected zone and the middle of the weld, 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 joint with a hard and brittle structure, in order to improve its toughness and plasticity, reduce its hardness, and obtain the appropriate coordination of hardness, strength, plasticity and toughness, the welding joint must be properly tempered. After heat treatment, the brittleness of the heat affected zone should be eliminated, and the base material should be able to maintain a certain strength and elasticity. Tempering is carried out in a 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. Three specimens of each tempering treatment are taken, and the average value of their tension is taken.

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, but not 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 in the test is 1 663 MPa). 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 preservation is held for 10 min, 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. The microhardness of each zone of the longitudinal profile was tested along the axis of the 280℃ tempered welding head. 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 hardness. The welded ring wire should not only meet the requirements of strength and elasticity, but also have a certain fatigue strength