Welding technology as a traditional processing technology after a century of development, the application fields of industries, welding processes nearly a hundred, in machinery manufacturing, aerospace, automotive, electronics and other industries have become the other connection can not be replaced technology. In particular, China is still in the process of industrialization in steel production and consumption are far in the world, welding technology still plays a very important role. Throughout the industrialized countries, steel is welded with power power.

Hot-rolled plate products are mainly used in shipbuilding, building structures, bridges, boilers and pressure vessels, pipelines, offshore platforms, construction machinery and other important occasions, so the quality of the product, welding requirements are also increasing. This requirement in the following areas:

(1) satisfy the strength, toughness indicator;
(2) excellent service performance, including resistance to high and low temperature performance, anti-fatigue properties, corrosion resistance and other media;
(3) Good welding performance, including a wide range of welding process adaptability, high resistance to crack resistance, suitable for large heat input welding;
(4) comply with the regulations;

One of the requirements of the Welding Electrode is one of the most important, but also iron and steel production enterprises in their efforts to solve the key technology. Micro-alloyed steel products to improve and enhance the weldability of the core.

Smelting and rolling technology advances

A clean steel technology

Without micro-alloying the overall progress of metallurgy, hot metal pretreatment, BOF, ladle refining, vacuum refining refining technology used to make steel in S, P and other impurities content is much lower than the previous low-carbon steel and low-alloy steel.

To performance, for example, the current pure steel smelting technology can achieve the following levels:

[P + S + N + O + H] ≤ 80ppm

P ≤ 20ppm, S ≤ 5ppm, N ≤ 20ppm, O ≤ 10ppm, H ≤ 1.0ppm

With the significant reduction of impurity elements, along with crystal greatly reduced the incidence of cracks, is no longer a concern and focus of the study.

As the use of structural design requirements, the plate thickness direction of the performance can not be ignored. Elimination of segregation in continuous casting technology is improving the middle, greatly reduce the degree of segregation, to improve the performance of Z-plate.

2 controlled rolling and controlled cooling

Controlled cooling technology to promote technological progress rolling, controlled rolling and controlled cooling so that the effective integration, combined with the result that the steel components easier, steel to further improve overall performance. At the same time as the automation and control technology in rolling applications continue to mature, qualified to produce high-quality, high-precision products. Micro-alloying technology combined with controlled rolling and cooling, to achieve the controlled state thermomechanical treatment, with strain hardening, precipitation hardening and strengthening the combined effect of phase change, get more than alloying, normalizing and quenching, better plastic, low temperature toughness, high strength, more importantly, because the carbon equivalent Ceq and Pcm of the lower crack sensitivity index, welding performance greatly improved gradually from easy to be welded to the welding direction.

Thick hot rolled steel plate is currently widely used to control rolling (TM) with normalizing rolling, controlled rolling (also known as CR, a two-stage three-stage rolling and rolling); control the cooling process has accelerated cooling ( ACC) and the direct quenching (DQ); controlled rolling and controlled cooling process to form TMCP process.

Japan TMCP process has been used to produce the structure of the yield strength 570MPa steel for bridges, pressure vessels and pipelines, and 75mm steel plate welded to ensure no warm-up, no crater cracks. At the same time using the same technology being developed 690MPa yield strength of structural steel.

Advantage of the new micro-alloy steel welding

Using TMCP technology, has developed a variety of foreign high-strength structural steel welding. More typical of steel are:

(1) Nippon Steel yield strength 420MPa development and production of steel (in accordance with API 2WGr.60), thickness 40 ~ 70mm, PWHT Akv (-40 ℃) 280J, and FATT to -90 ℃ ~ -100 ℃, Akv150J for offshore platforms; followed the development of oxide dispersion of the distribution of yield strength 500MPa steel for offshore platforms.

(2) Kawasaki Steel and Kobe Steel, Ltd. has developed a yield strength of 570MPa steel, Mig Welding Rod heat input of up to 200KJ/cm (traditional steel four times), -20 ℃ to use, welding without preheating, no crater cracks without hardening, thickness up to 75mm, compared with the SM570 has obvious advantages for the bridge construction, and without coating.

(3) Nippon Steel and titanium nitride using titanium dioxide dispersed technology (HTUFF-Super HAZ Toughness Technology with Fine Microstructure Imparted by Fine Particles) development of earthquake-resistant building steel 490MPa, 520MPa, 590MPa series, the maximum thickness of 100mm, welded heat Enter up to 1000KJ/cm, local brittle weakened.

(4) Finland using TMCP + ACC technology, production NVE360, NVE400, NVE500, for icebreakers,, NVE400, NVE500, for icebreakers, NVE500 of Ceq 0.40%.

From the above examples can be found, the development of modern rolling technology to bring low-cost iron and steel enterprises (alloy added less), the main thing is for the downstream users of steel production to provide more direct benefits.