Steel Pole Industry about Selection of Q235B and Q345B
Q235B and Q345B materials are commonly used in track-type bulldozers. Under the premise of meeting the design requirements, Q345B is used instead of Q235B to reduce costs. Firstly, the chemical composition and mechanical properties of the two materials are compared, and then the welding process test of the same welding parameters is carried out, and the obtained test data is analyzed, and the Q235B material is replaced by reducing the thickness of the Q345B material under the same structural performance requirements. Achieve the effect of reducing costs.
1 Overview
With the continued downturn in the construction machinery market in recent years, the sales volume of construction machinery products has gradually declined. In today's market situation, Shantui has also been affected as the country's largest manufacturer of crawler bulldozers. In order to reduce the production cost and increase the economic benefit, combined with the structure and mechanical properties of the bulldozer, a reasonable selection of Q235B and Q345B materials was proposed through continuous analysis and research.
Through the analysis of the chemical composition and mechanical properties of Q235B and Q345B materials, it is proposed that Q345B material can be used to replace part of Q235B material in the bulldozer structural parts. Under the requirement of satisfying the mechanical properties of the bulldozer structural members, the thickness of the steel plate can be reduced and the materials used can be reduced. The weight, to achieve the role of reducing costs and increasing efficiency.
2. Comparison of the two materials
The chemical composition of the Q235B and Q345B materials is shown in Table 1. The mechanical properties are shown in Table 2.
Table 1 Comparison of chemical composition of Q235B and Q345B materials
Table 2 Comparison of mechanical properties of Q235B and Q345B materials
According to the total amount of Q235B and Q345B used by the company in 2011 and the annual output of 10 000 bulldozers using Q235B and Q345B, the consumption of the two steels is shown in Table 3.
Table 3 Q235B and Q345B material consumption
3. Test method
(1) Test materials According to the design requirements of the rear axle box design of the SD16 bulldozer, a large amount of Q235B and Q345B materials are used in the rear axle box structure, accounting for about 1/3 of the total weight of the rear axle box. Among them, the weight of Q235B steel plate in SD16 rear axle box is 125kg, and the weight of Q345B steel plate is 171.6kg.
(2) Welding process The welding process requires that the weld strength quality is Q/STB12.606-2000. The weld is cleaned and repaired. Specific welding parameters are shown in Table 4.
Table 4 Welding parameters
In the welding process, the welding parameters and process requirements of Q235B and Q345B are the same. Q235B belongs to carbon steel material, Q345B belongs to low alloy structural steel, and both materials are rolled by continuous casting billet. The difference is that the content of alloying elements is mainly reflected in the manganese content, wherein wMn=0.3% of Q235B~ 0.8%, wMn = 1% to 1.6% of Q345B. Both materials have good weldability.
Q345B has better comprehensive performance than Q235B. Among them, tensile test of 16mm thick plate shows that the tensile strength of Q345B material is ≥345MPa, and the tensile strength of Q235B material is ≥235 MPa.
Through the tensile and fracture tests of the weld after welding and the metallographic structure of the two welds tested, it is proved that the weld quality in both sets of tests meets the company standard (Q/STB12.606-2000). Quality requirements.
4. Analysis of economic benefits
According to the mechanical properties of Q235B and Q345B materials, the tensile strength of Q345B is 42.5% higher than that of Q235B. The thickness of the sheet can be reduced by using Q345B material instead of Q235B, thereby reducing the production cost. That is, a 10mm thick Q345B steel plate can be used instead of a 14mm thick Q235B steel plate. According to the consumption of the two materials listed in Table 3, according to the thickness and price of the sheet (see Table 5), according to the annual output of 5000 bulldozers, if half of the Q235B material is replaced by Q345B, the annual cost savings will be 3.873 million yuan.
Table 5 Q345B and Q235B price comparison
It can be seen from Table 3 that the weight of Q235B material for an annual output of 10 000 bulldozers is 12 880t, and the annual production capacity of 5000 bulldozer Q235B materials is 6440t. According to the principle that half Q235B is replaced by Q345B, the annual output of 5000 bulldozers Q235B The weight replaced by Q345B is 3220t.
The weight of the plate saved after replacing Q235B with Q345B is 1026.7t; after replacement, the weight of Q345B is 2193.3t.
According to the price of the two plates in Table 5, after half of the Q235B is replaced by Q345B, the annual cost of 5,000 bulldozers is 3.873.48 million yuan. Each bulldozer can save 775 yuan.
5 Conclusion
Through the comparison of the welding performance of the rear axle box of the track-type bulldozer and the economic benefit analysis, the following conclusions are drawn:
(1) After the Q345B material is replaced by Q235B material, the thickness of Q235B sheet is large, and the thickness of Q345B sheet is thin. It is necessary to modify the size, thickness and welding process (welding groove) of the part to meet the requirements of the design structure. Modify some tooling and fixtures.
(2) Use Q345B material instead of Q235B material, and replace half of Q235B material used by each bulldozer with Q345B, each saving 775 yuan; annual production of 5000 bulldozers can save 3.87 million yuan.
(3) It is recommended to use Q345B materials as much as possible in the future when designing and developing new products, and use Q235B less, which can not only meet the structural performance requirements of the products, but also reduce the production cost.
