Hot Dip Galvannealed Steel Sheet Production Method
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Solution Overview
Problem
Hot dip galvannealed steel sheets produced by existing methods, such as the Sendzimir method or non-oxidizing furnace method, suffer from reduced workability, elongation, and increased coil break due to high yield strength and solute carbon retention, leading to degraded performance in applications like automobiles.
Innovation Solution
A method involving hot rolling, pickling, cold rolling, continuous annealing, and specific temperature control during galvanization, including preplating with Ni or Ni-Fe without temper rolling, and controlled temperature rises to minimize solute carbon retention and prevent coil break, while maintaining excellent workability and slidability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the Sendzimir method or non-oxidizing furnace method is used to produce hot dip galvannealed steel sheet, then the steel sheet can be produced with standard工艺流程, but the solute C remains in large amount leading to high yield strength and degraded workability
Solution Approach 1:
The patent applies parameter changes by precisely controlling the temperature profile during alloying (heating rate of 20°C/sec or more to 460-550°C, holding for less than 5 seconds, then cooling at 3°C/sec or more) and compositional parameters (C: 0.01-0.12%, Mn: 0.05-0.6%, Si: 0.002-0.1%, sol. Al: 0.005-0.1%) to achieve optimal workability and surface properties
Solution Approach 2:
The patent applies preliminary action by performing preplating with Ni or Ni-Fe before galvanization, and by controlling the temperature pattern during alloying to prevent excessive carbide precipitation before the final product is obtained
2Stability of the object's composition
If temper rolling is performed at 0.6 to 1.5% elongation rate to prevent coil break, then the shape is corrected, but solute C adheres to dislocations causing strain aging and deteriorated workability
Solution Approach 1:
The patent reduces the temper rolling elongation rate from the conventional 0.6-1.5% to 0.4% or less, which is a parameter change that prevents excessive solute C adherence to dislocations while still maintaining shape stability and preventing coil break
Solution Approach 2:
The patent applies partial action by using a minimal temper rolling elongation rate (0.4% or less) that is just sufficient to prevent coil break without causing excessive strain aging, rather than using the full conventional range
3Manufacturing precision
If the alloying temperature is raised to 550°C or higher, then the alloying is sufficient, but the workability deteriorates due to strain aging
Solution Approach 1:
The patent lowers the alloying temperature from the conventional 550°C or higher to 460-550°C, combined with a rapid heating rate (20°C/sec or more) and minimal holding time (less than 5 seconds), achieving sufficient alloying while preventing strain aging
Solution Approach 2:
The patent uses a periodic action pattern in the temperature profile - rapid heating, brief holding, and rapid cooling - which allows sufficient alloying to occur during the brief high-temperature period while minimizing the time for strain aging to develop
4Temperature
If the heating rate is slow during alloying, then the temperature can be maintained, but the solute C adheres to dislocations causing strain aging
Solution Approach 1:
The patent uses periodic action with a rapid heating rate (20°C/sec or more) followed by brief holding (less than 5 seconds) and rapid cooling (3°C/sec or more), which maintains temperature stability during the critical alloying period while minimizing strain aging through the brief exposure time
Solution Approach 2:
The patent applies the skipping principle by rushing through the critical temperature range (460-550°C) as quickly as possible with a heating rate of 20°C/sec or more and holding for less than 5 seconds, minimizing the time solute C can adhere to dislocations while still achieving sufficient alloying
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method produces hot dip galvannealed steel sheets with minimal deterioration in elongation, improved workability, and enhanced powdering and slidability, effectively addressing the limitations of existing production methods.
Implementation Method 1
heating by 5°C/sec or more down to 430 to 500°C, galvanizing in a galvanization bath, wiping, then heating by a rate of temperature rise of 20°C/sec or more up to 460 to 550°C
Implementation Method 2
cooling to 250 to 450°C, holding at said temperature range for 120 seconds or more, then cooling to room temperature
Implementation Method 3
annealing at 650 to 900°C
Data Source
AI summary
The present invention provides a method of production of hot dip galvannealed steel sheet with excellent workability compared with the Sendzimir method or non-oxidizing furnace method and further with excellent powdering or slidability, that is, a method of production of hot dip galvannealed steel sheet with excellent workability, powdering, and slidability characterized by processing a slab containing, by mass %, C: 0.01 to 0.12%, Mn: 0.05 to 0.6%, Si: 0.002 to 0.1%, P: 0.05% or less, S: 0.03% or less, sol. Al: 0.005 to 0.1%, and N: 0.01% or less and having a balance of Fe and unavoidable impurities by hot rolling, pickling, cold rolling, then annealing at 650 to 900° C., cooling to 250 to 450° C., holding at said temperature range for 120 seconds or more, then cooling to room temperature, pickling, preplating Ni or Ni—Fe without intermediate temper rolling, heating by 5° C./sec or more down to 430 to 500° C., galvanizing in a galvanization bath, wiping, then heating by a rate of temperature rise of 20° C./sec or more up to 460 to 550° C., not providing any soaking time or holding for soaking for less than 5 seconds, then cooling by 3° C./sec or more, and final temper rolling by a 0.4 to 2% elongation rate.